Method for making a surgical suturing needle

Abstract: A surgical suturing needle is formed to have a needle shaft with a rectangular cross-section and a needle head with a triangular needle point. A transitional portion between the needle shaft and the needle head is formed to have a maximum width greater than the width of the needle shaft. A plurality of cutting edges extend from the needle point to at least the maximum width section of the transitional portion. After forming and grinding the suturing needle, it is immersed in an acid bath and exposed to an electrical field. Finally, the surgical needle is heat-treated to increase its strength and resistance to bending or breaking.

Description: The present invention relates to a method of manufacturing a surgical suturing needle that can be used generally for adjoining or closing adjacent portions of skin or tissue. More particularly, the suturing needle manufacturing process of the present invention is directed to a new class of suturing needle particularly suitable in plastic and reconstructive suturing applications. Suturing needles for applying sutures, or stitches, by hand in cutaneous and subcutaneous tissues are well known in the art. The sutures are typically used to close wounds or adjoin adjacent tissue, often at the conclusion of a surgical procedure. Conventional suturing needles are usually made from a cut blank of material such as stainless steel. The cut blank is metal-worked using well known machining techniques to form a surgical suturing needle. The needle generally includes a shaft, a rear end portion with means to grip or secure a suturing thread and a needle head at a front end portion for puncturing skin and tissue through which the needle travels. The needle head typically includes a sharpened needle tip at its distal end and cutting edges. Needle sharpness is an important consideration in designing and manufacturing surgical suturing needles. Sharper needles require less force to penetrate the tissue and thus cause less tissue trauma. In addition, sharper needles reduce fatigue on the needle itself, making it less likely to bend or break during suturing. Needle sharpness is typically defined in terms of a so-called penetration force -- the force necessary for a needle point to puncture, or penetrate, the tissue. The penetration force is primarily determined by the design and sharpness of the needle point. However, needle sharpness is also affected by a drag force of the needle as it travels through the tissue. The ability of the needle to pass smoothly through the tissue is a desirable characteristic. The drag force of the needle depends upon the design and sharpness of the needle, especially the needle head. The quality of a lubricating coating on the needle also affects the drag force. For example, if the lubricating coating on the needle wears off, the drag force on the needle increases with each pass of the needle through the tissue. This effect could give the surgeon-user the false impression that the needle is failing to retain its sharpness. Another important consideration in designing and manufacturing surgical suturing needles is their resistance to bending or breaking during use. The strength of a suturing needle is a measure of its ability to resist bending and is determined by such factors as (a) the material selected to make the needle, (b) the cross-sectional shape of the needle, and (c) the heat treatment process received by the needle during manufacturing. However, needle strength should be balanced by needle ductility, which is defined in terms of the ability of the needle to be reshaped after it flexes from its original shape. A surgical needle with good strength characteristics but having little or no ductility can be brittle and may snap and break during use. In use, the surgical needle is held at its rear end by a needle holder and the needle tip is forced against the tissue to be sutured. This action creates a bending moment on the needle body, and a needle with some degree of ductility will be able to be reshaped to its original shape without breaking. It is generally known that in working with a metallic material, as the strength of the material increases the ductility will decrease. Therefore, it is desirable to carefully balance the strength and ductility characteristics of a suturing needle. Another desirable attribute is stability of the suturing needle in a needle holder. The needle holder is typically used to grip and stabilize the needle as it passes through the tissue. The subject invention provides significant advances over conventional surgical suturing needles manufacturing methods by improving needle attributes such as needle sharpness and resistance to bending or breaking during use as well as other desirable attributes. A prior art needle manufacturing technique is disclosed in DE-A-3434218, where a conventional shape needle is processed having a continuously decreasing head cross-section. Accordingly, it is a general object of the present invention to provide an improved method for making surgical suturing needle. It is another object of the present invention to provide a surgical suturing needle manufacturing process that will improve the resistance of the needle to bending and breaking and increase the ease with which it penetrates and travels through skin and tissue. These objects are achieved by the method of manufacturing a surgical suturing needle head of the present invention as defined in claim 1. The dependent claims 2-4 define preferred additional steps for manufacturing a needle in accordance with the present invention. These and other objects, aspects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. Figure 1A is a plan view of a surgical suturing needle; Figure 1B is a cross-sectional view taken at plane 1B-1B of the surgical suturing needle illustrated in Figure 1A; Figure 1C is a cross-sectional view taken at plane 1C-1C of the surgical suturing needle illustrated in Figure 1A; Figure 2A is a plan view of the surgical suturing needle which may be manufactured by the method of the present invention; Figure 2B is a cross-sectional view taken at plane 2B-2B of the surgical suturing needle illustrated in Figure 2A; Figure 2C is a cross-sectional view taken at plane 2C-2C of the surgical suturing needle illustrated in Figure 2A; Figure 3 is an elevational view of the surgical suturing needle; Figure 4 is a plan view of the surgical suturing needle; Figure 5A is an elevational view of a cut blank used to form the surgical suturing needle; Figure 5B is a cross-sectional view taken at plane 5B-5B of the cut blank illustrated in Figure 5A; Figure 6A is an elevational view of a coined preform used to form the surgical suturing needle; Figure 6B is a cross-sectional view taken at plane 6B-6B of the coined preform illustrated in Figure 6A; Figure 7 is a front elevational view of a coined preform used to form the surgical suturing needle; and Figure 8 is a table showing comparable data between a surgical suturing needle manufactured by the method of the subject invention and two conventional needles. The surgical suturing needle of the present invention is manufactured to possess attributes of primary importance in suturing needles. For example, the suturing needle is designed with superior needle sharpness to penetrate and travel easily through the cutaneous and subcutaneous layers of tissue. The surgical needle also has superior strength and resistance to bending and/or breaking during use. In achieving these desirable characteristics, a threefold approach is used to produce the surgical suturing needle. As discussed below, each component of this three-fold approach is interdependent, and is preferably used in conjunction with the other components to achieve an optimum suturing needle. The first component is proper selection of the material for the surgical needle to obtain superior physical characteristics. Second, the needle is designed in a way to enhance its penetration characteristic and the ability to travel through the tissue and to provide it with superior physical characteristics, and third, particular manufacturing steps are used in metal-working the needle to achieve optimum benefits of the needle design. The choice of materials is of primary importance to the physical characteristics, that is, strength, ductility and resistance to bending or breaking of the needle. However, the cross-sectional shape and dimensions of the needle and the heat-treating process which the needle receives during the manufacturing process also contribute to the physical characteristics of the needle. The suturing needles are preferably made from AISI 302 type stainless steel. However, AISI types 301 or 304, which possess similar characteristics to AISI 302, can also be used. These '300' series stainless steels, which typically have a tensile strength of 228702940 - 246295470 kg/cm 2 (325,000-350,000 lbs/in 2 ),attain their high strength from undergoing cold working as the material is converted from an ingot to wire of the desired diameter. The design of the surgical needle contributes to both its strength and resistance to bending and to its ability to easily pierce and travel through the tissue to be sutured. The finished needle 10 is shown in Figure 1A to have a curved needle shaft 12 with a needle head 14 at its distal end and a rear end portion 16 at its proximal end. The needle head 14 terminates in a needle point 18 for piercing the skin or tissue. The rear end portion 16 includes an axial hole 20 for receiving and securing a suturing thread. Of course, other means for securing the suturing thread within the proximal end of the needle shaft, such as for example, a crimping channel, are also contemplated. In accordance with the subject invention, the cross-sectional area of the needle shaft 12 is rectangular in shape as shown in Figure 1B. While conventional needles typically have cross-sections that are round or triangular, the rectangular cross-section provides strength superior to that of conventional cross-sections over the same area. The major axis A-A of the rectangular cross-section is in the plane of curvature, i.e, the X-Y plane, of the needle and the minor axis B-B lies in the X-Z plane (as seen in Figures 1A and 2A). Although an excessively pronounced rectangular shape can further increase the strength of the needle, such a cross-sectional shape reduces the stability of the needle in a needle holder. Therefore, it is preferable to shape the rectangular cross-section to have a major axis to minor axis ratio of 1.2 or less. As best seen in Figures 3 and 4, the needle head 14 is shaped to have three sides 22 tapering toward the distal end of the needle to form the needle point 18. The cross-section of the needle point is triangular in shape as shown in Figures 1C and 2C, and the three corners of the triangle, that is, the edges adjoining each adjacent side 22, form cutting edges 24 for slicing the cutaneous and subcutaneous tissue. The included angle A of the needle point is preferably between 25° and 29° as shown in Figure 3. A smaller included angle would reduce the necessary penetration force but would also increase the susceptibility of the needle point to damage during fabrication or use. On the other hand, a larger included angle increases the durability of the needle point but also requires an undesirable increase in force necessary to penetrate the cutaneous tissue. The needle head 14 manufactured with the method of the subject invention features a cobra head shape, wherein the widest portion of the needle head has a width W 2 slightly greater than the width W 1 of the needle shaft as shown in Figure 3. The widest portion of the needle head 14 is identified as transition portion 21 in Figures 3, 4 and 7. Moreover, the cutting edges 24 extend from the needle point 18 to at least the widest part of the needle head 14. In this manner, the three cutting edges 24 slice the tissue as the needle head passes therethrough and provide an opening slightly larger than the shaft 12 of the needle, thus significantly reducing the drag force, and allowing the shaft to pass easily through the tissue. The length of the cutting edges are preferably between 3 and 7 times the diameter of the wire, or cut blank, used for the needle. The manufacturing process of the subject invention preferably begins with selection of a cut blank from a coil of wire made of one of the preferred materials discussed above. The cut blank 26 is shown in Figure 5A, and has a conventional round cross-section 27 as shown in Figure 5B. The cut blank is worked with a conventional press or swaging machine to form the needle shaft 12 with a rectangular cross-section 13 as shown in Figures 6A and 6B. As shown in Figures 6A and 7, the proximal end 16 of the needle shaft can retain its circular cross-section, and is machined to provide an axial hole 16, or other comparable means, for securing the suturing thread to the needle. After the shaft is formed, the three-sided needle head 14 is formed at the distal end by using, for example, a three-jaw toggle press or a swaging machine. The three sides 22 are first worked to form a blunt end "cobra-head" type shape with transition portion 21 having a maximum width W 2 slightly larger than the width W 1 of the needle shaft 12 as described above. The cutting edges 24 will also necessarily be curved as shown in Figure 6A, as the three-sided needle head 14 meets with the four-sided needle shaft 12. A coined preform of the suturing needle is thus formed at the manufacturing stage shown in Figures 6A and 7. Progressively finer grinding media, such as an abrasive belt, are then used to finish shaping the cobra head and form a needle point 18 at the distal end of the needle head. The needle point and cutting edges are further honed to form sharp cutting edges. The use of progressively finer sharpening media minimizes any burr formation on the cutting edges of the needle head. The surgical needle is then curved to its appropriate shape at this stage of the manufacturing process by conventional means, making sure the major axis of the rectangular cross-section is in the plane of curvature of the needle as described above with reference to Figures 1A, 1B, 2A, and 2B. As will be appreciated, the particular radius of curvature of the needle is a matter of design application and user preference. The surgical needle is then exposed to an electrical field while being immersed in an acid bath. This electrochemically processing step removes any burrs left from the grinding process and smooths without dulling the cutting edges of the needle head. While the actual amount of material removed in this step is very small, electrohoning can reduce by 30% to 40% the force necessary to penetrate the tissue. The time of exposure, temperature of the acid bath and the current density of the electrical field should be carefully controlled to obtain the maximum benefit of this step. For example, when using AISI 302 type stainless steel as the material for the needle, the temperature of the acid bath is preferably within a range of 54,4°C to 82,2°C (130° to 180°F), and more preferably around 66°C (150°F), the time of exposure can range from 3 to 20 minutes, with 8½ minutes found to be the optimum exposure time, and the preferred current density is 430.56 amps/m 2 (40 amps/ft 2 ), although a broader range of between 107.64 and 861.11 amps/m 2 (10 and 80 amps/ft 2 ) can be used depending upon the temperature of the acid bath and the time of exposure. The metal-worked, fully shaped needle may then be heat treated to increase its strength and resistance to bending. In the heat treating step, the needles are exposed to a temperature of 371,1°C to 593,3°C (700° to 1100°F), and preferably between 426,67°C and 482,22°C (800° and 900°F), for a time period of between 1 to 4 hours. The heat treated needles can then be coated with a lubricant to enhance passage of the needle through the tissue. Conventional solutions for this purpose include silicones and Teflon. Each component of the three-fold approach describe above, that is, material selection, needle design and the manufacturing process, are interdependent. Recognizing the interdependency of these components produces a superior surgical suturing needle that provides optimum performance. Figure 8 shows a table illustrating the comparative results of four groups of different sized needles. Each group contains a suturing needle made in accordance with the subject invention, identified by source as "D + G", and two conventional models. The first conventional needle in each group is marketed by Sulze and is shaped to have a three-sided needle head design and a body shape with a triangular cross-section. The second conventional needle in each group is marketed by Ethicon and has a three-sided needle head design and a round body shape with flattened top and bottom portions. Some of the Ethicon needles also have a 'cobra-head' type head design. As the table shows, the first measurement of needle performance, penetration force, is lowest in each group for the needles made in accordance with the subject invention. The penetration force was measured using an average of 10 needles per lot, with three penetrations per needle through rabbit skin. As will be appreciated, lower penetration force is desirable, as this indicates superior needle sharpness and reduces tissue trauma. The second measurement of needle performance is strength as measured in a moment force needed to bend the needle. This test was performed using a Tinius-Olsen Tester with an average of 10 needles per lot. As the table in Figure 8 illustrates, the 'D + G' needles required a greater moment force to bend the needles. Lastly, ductility was measured in the number of times a needle could be manually bent through 30° on either side of a nominal position without breaking. Again, an average of 10 needles per lot were tested. The needles obtained by the subject invention demonstrated superior ductility over conventional needles by withstanding a greater number of bends before breaking.

Claims: A method for forming a surgical needle head on a needle shaft in the manufacture of a curved surgical suturing needle (10) wherein the needle shaft (12) of the needle (10) has a width (W 1 ) and a rectangular cross section (Figs. 1B, 2B) with a major axis (A-A) lying in the plane of curvature of the needle (10) and a minor axis (B-B), said major axis (A-A) and minor axis (B-B) having a ratio of 1.2 or less, wherein the needle head of the needle (10) is a multi-sided needle head (14) having a needle point (18) with an included angle of between 25° to 29° and a plurality of cutting edges (24) extending axially from said needle point (18) and defining sides (22) of said needle head (14), and wherein the needle has a transitional portion (21) adjoining said needle shaft (12) and said needle head (14), with said transitional portion (21) having a maximum width (W 2 ) greater than the width of said needle shaft (12) corresponding to the minor axis (B-B) and said method comprising the steps of: (i) metal-working one end of the needle shaft to form a three-sided needle head terminating in a needle point, with the needle head having a plurality of cutting edges and a triangular cross section; and (ii) forming a transitional portion on the needle head between the needle point and the needle shaft, with the transitional portion having a width larger than a width of the needle shaft, wherein the cutting edges extend axially from the needle point to at least the transitional portion of the needle head. A method of making a surgical suturing needle according to claim 1, further comprising the step of applying a lubricating coating to the needle. A method of making a surgical suturing needle according to claim 1, further comprising the step of bending the needle shaft to form a curved needle. A method of making a surgical suturing needle according to claim 1, further comprising the step of electrochemically processing the needle by placing it in an acid bath while exposing it to an electrical field.

Inventors: BUZERAK JOHN E, KAPRALOS PAUL, MAURER ROBERT, PRASAD JANNAIH S, PUTNAM CHARLES L, BUZERAK, JOHN E., KAPRALOS, PAUL, MAURER, ROBERT, PRASAD, JANNAIH S., PUTNAM, CHARLES L.
Applicants: AMERICAN CYANAMID CO, AMERICAN CYANAMID COMPANY
Application year: 1994
Main classification: A61B17
IPC codes: A61B17